S-Adenosyl methionine-dependent methylation reactions occur in all cells and modify a variety of biological molecules including nucleic acids, proteins, lipids, carbohydrates, and other small molecules. These reactions appear to be vital to many regulatory processes. Methyltransferases are known to comprise a somewhat homogenous family, with many having native molecular weight or subunits of about 30-kDa, and requiring a cysteine residue for activity. However, the structures of these enzymes and the details of the methyl transfer reaction remain poorly understood. The purpose of the proposed research is to investigate the structural- functional relationships of the S. typhimurium CheR S-adenosyl L- methionine; glutamyl methyltransferase, an enzyme that is essential to the regulation of the membrane receptor proteins involved in chemotaxis. An efficient CheR expression vector has been constructed which enables the rapid and easy purification of the enzyme from crude cell extracts. A vigorous effort will be made to obtain crystals of CheR which will lead to a determination of its structure by X-ray analysis. Attempts will be made to determine the identities of the amino acids that constitute the S-adenosyl-L-methionine and receptors binding sites. The amino acids that are crucial for enzyme activity will be investigated and their location will be ascertained using genetic as well as biochemical techniques.